1. Field of the Invention
This invention relates to a method of image formation using silver halide photographic materials and particularly to an improvement of adaptability to the developing agent in image formation based on silver halide lithographic type photographic materials.
2. Description of the Prior Art
Lithographic type (hereinafter, lith-type) photographic materials, comprising silver halide photographic emulsions having a very high contrast characteristic, are processed with a special type of extremely high contrast developer (hereinafter referred to as a lith-type developer) to provide a very contrasty image comprising half-tone dots and lines, and are used as photographic originals for printing plates.
A lith-type developer which is sometimes referred to as infectious developer from the mechanism of development involved can be supplied to the ultimate user in two different forms, i.e., either in a powder form in which a preliminary prepared powder is dissolved in water prior to use, or in a liquid form in which a concentrated solution is appropriately diluted for processing. Both types contain a dihydroxybenzene compound as a principal developing agent, an aldehyde-alkali metal bisulfite adduct, a small amount of a sulfite salt, etc.
In general, the powder type utilizes sodium carbonate as an alkaline material, while, on the other hand, the liquid type uses potassium carbonate as an alkaline material. Such selections are based on the fact that potassium carbonate is better suited for the liquid form because of its higher solubility.
Accordingly, these two types of developers have a different ionic strength in the final working solution, naturally causing different developing capabilities for the same photographic material.
For example, where one designes a certain type of photographic lith material so as to have a pre-determined sensitivity (photographic speed) when processed with a liquid type lith developer, the resulting film will exhibit a speed which is almost two times higher when such is processed with a powder type lith developer, and vice versa. Further, a lith film, which has been designed to exhibit a good dot reproducing capability when processed with a liquid type developer, will often exhibit a poor dot quality performance when a powder type developer is used, and vice versa.
On the other hand, a lith-type photographic material must be capable of being subjected to a mass scale, rapid processing; in other words, either mannual processing at a temperature below about 20.degree. C. or a rapid processing using an automatic processor at a temperature not less than about 25.degree. C. should desirably provide an image with a good dot quality together with a constant sensitivity (photographic speed).
Further, a photographic lith film should essentially not only provide an image of acceptable dot quality with a constant photographic speed unaffected by fluctuations in the composition or in the temperature of the developer, but also exhibit a desirable developing speed as well as an appropriate half-tone scale. (See Japanese Patent Application 64437/1974, and J. A. C. Yule, Principles of Color Reproduction, pp. 90 to 92, John Wiley & Sons Inc., (1967).)
To satisfy these requirements the effects of various compounds have been extensively investigated which are added to photographic emulsions or to processing agents.
As an example, a number of patents such as U.S. Pat. Nos. 3,294,540 and 3,471,297, British Pat. No. 1,107,022, Japanese Patent Publication 8586/1965, etc., disclose that polyoxyethylene compounds added to a silver halide emulsion layer can increase the image contrast and also improve dot quality.
However, it has still remained quite difficult to maintain the chief photographic characteristics (e.g., sensitivity (photographic speed), dot quality, half-tone scale, etc.) substantially unchanged with development under different conditions (e.g., with developers of different compositions, particularly of different ionic strengths or at different temperatures). Thus, when the process conditions differ, the exposure conditions must be correspondingly adjusted, or alternatively a series of lith films must be stocked, each of which has a different content of certain additives. This complexity, of course, gives rise to disadvantages and inexpediences in daily processing practice and on the manufacture of photographic materials.